1. Technical Field
This invention relates to touch sensors, and more particularly to rigid flat panel touch-sensitive sensors.
2. Background Information
Touch sensors or touch panels are used in various applications to replace conventional mechanical switches; e.g., kitchen stoves, microwave ovens, and the like. Unlike mechanical switches, these sensors contain no moving parts to break or wear out. Also, touch sensors are easily cleaned due to the lack of openings and cavities which tend to collect dirt and other contaminants.
Conventional capacitive touch sensing systems employ a passive form of detection. In such a sensor, a capacitive circuit is driven by a source signal. A key touch, representing a change to the circuit capacitance, results in attenuating the potential, and the resulting voltage level change indicates a key touch. This capacitive circuit is often implemented by the deposition of opposing conductive key pads to opposite sides of a dielectric element.
One problem with conventional sensors is that accumulation of foreign deposits on the key pads has the drawback of negating the effect of a touch by the user. Chemicals and abrasion of the exposed key pads may also degrade performance. Also, different dielectric characteristics, such as thickness and dielectric constant, often result in having to change or redesign the size of the key pads to achieve the same capacitance for a different dielectric element in identical applications.
Moreover, some known touch panels use a high impedance design which may cause the touch panel to malfunction when water or other liquids are present on the substrate. This presents a problem in areas where liquids are commonly found, such as a kitchen. Since the pads have a higher impedance than the water, the water acts as a conductor for the electric fields created by the touch pads. Thus, the electric fields follow the path of least resistance; i.e., the water. Also, due to the high impedance design, static electricity may cause the touch panel to malfunction. The static electricity is prevented from quickly dissipating because of the high touch pad impedance.
Also, many existing touch panels use additional elements, such as transistors, disposed integrally or proximate to each key pad, adding complexity to the touch sensor.
Thus, a need exists for an improved touch-sensitive sensor that addresses one or more of the drawbacks of the prior art.
According to an embodiment of this invention, a touch sensor detects manual contact by a user to actuate a controlled device. The touch sensor includes a substrate, an RF signal transmitter including a plurality of first conductors, and an RF signal receiver including a plurality of second conductors. The first and second conductors are located in spaced, interdigitated alignment with one another on the substrate, to form a key having a geometry which affords substantial coverage thereof by a human appendage. The RF signal receiver includes an RF signal amplifier electrically coupled to the second conductors. A processor is electrically coupled to the RF signal receiver to detect variations in signal strength corresponding to coverage of the key by a human appendage to selectively actuate the controlled device.
In another embodiment of the inventions, a touch sensor is provided to detect user contact to actuate a controlled device. The touch sensor includes a substrate, an RF signal transmitter including a RF signal generator and plurality of first conductors, and an RF signal receiver including a plurality of second conductors. The first and second conductors are disposed in spaced, interdigitated alignment with one another on the substrate, to form a key having a geometry which affords substantial coverage thereof by a human appendage. The RF signal receiver includes an RF signal amplifier electrically coupled to the second conductors. A processor is electrically coupled to the RF signal receiver to detect variations in signal strength corresponding to selective coverage of the key by a human appendage to selectively actuate the controlled device. The RF signal receiver receives a baseline signal when the first and second conductors are free from the coverage, and the RF signal receiver receives an activation signal which is discrete from the baseline signal upon the coverage. An absolute value of the activation signal is less than an absolute value of the baseline signal.
In a still further embodiment of the present invention, a method is provided for detecting manual contact by a user to actuate a controlled device. The method includes the steps of providing a substrate, providing an RF signal transmitter including a two or more first conductors, and providing an RF signal receiver including a two or more second conductors coupled to an RF signal amplifier. First and second conductors are located in spaced, interdigitated alignment with one another on the substrate, to form a key having a geometry which affords substantial coverage thereof by a human appendage. A processor is electrically coupled to the RF signal receiver. The processor is used to detect variations in signal strength corresponding to selective coverage of the key by a human appendage to selectively actuate the controlled device.